The long-term objective of this research proposal is to analyze systematically the relationship between Ia antigen structure and the effect of this structure on regulation of the immune response. Transfer of responder alpha or beta chain genes into non-responder embryos will be used to produce transgenic mice capable of responding to the antigen in question. When the critical chain for response to a particular antigen has been determined, a series of allelic hypervariable region switch constructs will be produced and introduced into non-responder embryos to test the role of critical allelic hypervariable regions in mediating responsiveness to a particular antigen. By systematically introducing responder allelic hypervariable regions into the non-responder sequence, it will be possible to test the hypothesis that the allelic hypervariable regions are critical residues and, quite probably, contact residues for interaction with foreign antigen and the T cell receptor. These experiments will generate a series of mutants analogous to the A beta bm12 mutant in which discrete alterations in a single allelic hypervariable region can be tested in vivo for their functional effects on the development of immune responsiveness. A related series of experiments, also utilizing transgenic mouse models, will attempt to analyze the role of specific allelic sequence versus the role of ectopic site and level of expression of Ia antigens in the induction of autoimmunity. Finally, a series of experiments will be conducted in an attempt to develop anti- sense constructs for I-A beta sequences which can be used in the transgenic mouse model to "turn off" specific genes. Successful development of this approach would permit an analysis of the relative roles of Ia antigens expressed in normal and ectopic sites, of mediators such as gamma interferon and BSF1 , and of other gene products in the development of autoimmunity in animal models of autoimmune disease. These experiments should permit a detailed analysis of the role of class II MHC antigen structure in regulation of specific immune responses and in determining susceptibility to autoimmune disease. Analysis of the relative roles of specific allelic sequences versus ectopic expression of class II MHC antigens and the development of antisense approaches to analyzing the effects of particular genes in susceptibility to autoimmunity should permit the development of new therapeutic approaches to a wide variety of autoimmune diseases.